Method of processing a color cathode-ray tube

ABSTRACT

In one step of the screening process, the shadow mask of a color tube is mounted from studs provided in the faceplate section. The faceplate is then introduced into an exposure chamber where it is supported at three points spaced along the sealing land near the locations of the support studs. This establishes the faceplate in a reference mode, free of twisting moments and elastic deformation. When the screening process is completed, the faceplate is superposed over the enlarged end of the funnel section of the tube envelope and supported therefrom at three spaced points similarly disposed along the sealing land of the funnel to engage the faceplate at the same spaced points of support effective in the exposure step. This re-establishes the faceplate in its reference mode. Frit sealing material is disposed between the sealing lands of the envelope sections and the assembly is heated to seal the faceplate and funnel to one another along the entirety of the sealing lands.

United States Patent 1 Palac 1 Jan. 29, 1974 METHOD OF PROCESSING ACOLOR CATHODE-RAY TUBE [75] Inventor: Kazimir Palac, Carpentersville,Ill.

[73] Assignee: Zenith Radio Corporation, Chicago,

22 Filed: Feb. 7, 1973 21 Appl.No.:330,374

Related US. Application Data [62] Division of Ser No. 138,073, April 28,1971, Pat.

Primary ExaminerRoy Lake Assistant ExaminerJ. W. Davie Attorney, Agent,or Firm-Cornelius J. OConnor; John J. Pederson [5 7] ABSTRACT In onestep of the screening process, the shadow mask of a color tube ismounted from studs provided in the faceplate section The faceplate isthen introduced into an exposure chamber where itis supported at threepoints spaced along the sealing land near the 10- cations of the supportstuds. This establishes the faceplate in a reference mode, free oftwisting moments and elastic deformation. When the screening process iscompleted, the faceplate is superposed over the enlarged end of thefunnel section of the tube envelope and supported therefrom at threespaced points similarly disposed along the sealing land of the funnel toengage the faceplate at the same spaced points of support effective inthe exposure step. This re-establishes the faceplate in its referencemode. Frit sealing mate rial is disposed between the sealing lands ofthe envelope sections and the assembly is heated to seal the faceplateand funnel to one another along the entirety of the sealing lands.

4 Claims, 6 Drawing Figures PAIENTED JAN 2 9 I974 SHEET 1 8F 2 METHOD OFPROCESSING A COLOR CATHODE-RAY TUBE RELATED APPLICATION This applicationis a division of application Ser. No. 183,073, filed Apr. 28, 1971, nowUS. Pat. No. 3,737,065 by the present applicant for AN ENVE- LOPE FOR,AND METHOD OF PROCESSING, A COLOR CATHODE-RAY TUBE, which is assigned tothe same assignee as the present application.

BACKGROUND OF THE INVENTION Color cathode-ray or picture tubes come in avariety of sizes and shapes and are formed of a multisection envelope ofwhich the faceplate and funnel are major components. The faceplate has ascreen area and a circumscribing flange the free end of which serves asa sealing land. The edge at the large end of the funnel likewiseconstitutes a sealing land which matches the faceplate with respect tosize and configuration. While tubes may be round or rectangular, therectangular shape is currently the more popular.

The envelope is sectioned, as described, to facilitate the applicationof various phosphor materials to constitute an image screen. Here again,there is a choice as to structure but usually the screen is aninterlaced pattern of green, blue and red phosphors. They may be arrayedin a repeating sequence of stripes or, more usually, they may bephosphor dots collectively defining a multiplicity of color triadsregularly disposed throughout the screen area. 4

The screen is photographically printed in a process that is very wellknown. Basically, a photoresist material which becomes insoluble inwater upon exposure to actinic energy, such as ultraviolet light, isprepared as a slurry having one phosphor material suspended therein. Thefaceplate is given a coating of the slurry and the color-sectionelectrode or shadow mask is then installed in position within it.Thereafter, this subassembly is put into a lighthouse or exposurechamber where the slurry layer is exposed to light through the shadowmask. This creates a latent image of the pattern of that phosphor whichis subsequently developed by removing the shadow mask and washing thepanel with water. Repeating this general process three times, utilizingdifferent phosphor slurries on each occasion and appropriatelypositioning the exposure light source, accomplishes photographicprinting of all three phosphors materials on the screen after which thefaceplate and funnel sections are united to one another.

Integrating these envelope sections is a well known technique employinga frit type of glass-sealing material. The frit is usually applied tothe sealing land of the funnel with the funnel supported in a generallyvertical position and the faceplate is then superposed thereover withthe two sealing lands in registration with one another. The envelopeassembly is then heat treated in an oven having an appropriate heatprofile and time cycle to permit the frit to establish a vacuum typeseal all along the sealing lands of the faceplate and funnel.

This entire process is well understood and is successfully practiced inthe production of shadow mask color tubes on a mass production basis.Great care is exercised in the fabrication of the component parts and inthe various processing steps to assure proper and precise beam landingsin the finished tube. For example, the sealing lands of the faceplateand funnel are frequently precision ground in an effort to attain anoptimum mating of these sections in the sealing process. And yet, beamlanding errors are encountered.

If the tube in process is of the shadow mask variety with phosphor dottriads to be excited by a cluster of three electron guns, the threebeams ideally are concentric with the phosphor dots on which theyimpinge. Deviation from this condition of registration is theconditioned referred to as a beam landing error. It has been suspectedheretofore that the sealing edge of the faceplate pane] experiencesviscoelastic deformation in the sealing cycle resulting in a shift ordisplacement of the mask relative to the panel and consequentlyproducing beam landing errors. This conclusion was reached because itwas observed that there was very little, if any, shift of the maskrelative to the screen as the faceplate panel was introduced into thevarious exposure chambers required in processing the three phosphors buta shift did result when the panel was placed on the funnel and sealed.

Applicant has discovered that viscoelastic deformation is not the causeof the mask to panel shift and has further determined that the panelexhibits the property of elasticity to a sufficient extent that, even atambient temperatures, the sealing land of the panel accommodates orconforms to the specifics of the sealing land of the funnel and for thisreason is a principal source of beam landing error. The presentinvention obviates or minimizes this aspect of beam-spotmisregistration.

Accordingly, it is an object of this invention to provide a newfabricating technique, for color picture tubes which reduces beamlanding errors.

It is another object of the invention to provide a novel color tubeenvelope in the processing of which superior results are attained inrespect of beam landing errors.

Another specific object of-the invention is to improve the processing ofcolor picture tubes to reduce beam landing errors.

SUMMARY OF THE INVENTION An envelope for a color cathode-ray tube inaccordance with the invention comprises a faceplate section having animage area and a circumscribing flange the free end surface of whichconstitutes a first sealing land of a given size and configuration. Thefunnel section of the envelope likewise has a free end surface, usuallyits large end, which constitutes a second sealing land corresponding insize and configuration to that of the faceplate. At least one of theseenvelope sections has a plurality of spaced supports projecting from anddisposed along the sealing land thereof for achieving support of thefaceplate at spaced points as distinguished from the linear or planarsupport of prior envelope structures.

The processing aspect of the invention includes the steps ofphotographically printing the screen with different phosphor materials,essentially as described above, in which process the faceplate, with thecolorselection electrode or mask supported within it, is exposed whilebeing supported at three spaced points along its sealing land,establishing the faceplate in a reference mode in which the panel isfree of deformation and twisting moments. After the printing step, andwith the funnel substantially vertically disposed with its sealing landuppermost, the faceplate is placed on the funnel with the two sealinglands facing and in registration with one another, with a frit-sealingmaterial disposed between the sealing lands, and with the faceplatesupported from the funnel through a plurality of spaced contactsdisposed along the sealing lands to reestablish the faceplate in itsaforesaid reference mode. This assembly is then subject to heattreatment to seal the faceplate and funnel to one another along theentirety of the sealing lands.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a portion of an exposurechamber and the faceplate section of a picture tube in process;

FIG. 2 is a plan view, partially broken away, of the faceplate in theexposure position;

' FIG. 3 is a sectional view taken along line 3-3 of FIG. 2;

FIGS. 4 and 5 represent steps in the sealing of the faceplate and funnelsections;

while FIG. 6 shows a novel form of funnel section.

DESCRIPTION OF THE PREFERRED EMBODIMENT supporting the shadow mask tofacilitate its insertion and removal as required in various stages ofmanufacture, especially during screening. The free end 10d of thefaceplate constitutes a sealing land of a given size and configuration;for the case under consideration it is rectangular in shape and may be23 inches in diagonal dimension.

The color-selection electrode or shadow mask 11 has a multiplicity ofapertures 11a uniformly distributed over a rectangular field and a frame11b to which the apertured component is attached. Mounting springs 110are secured at one end to the frame and have an aperture at the free endfor engaging mounting studs 100 to psoition the mask within faceplate 10with a desired spacing relative to screen 10a. Both three and four pointsuspension systems are known but, for the case illustrated, only threemounting springs are employed. One is located in the central part of theuppermost periphery of the mask and the other two are locatedsymmetrically on the two sides of the mask with the apertured endsdisposed below the central axis. This is a conventional structure whichis easily inserted into and removed from faceplate 10. As describedbelow, phosphor dots are photographically printed on screen area 10athrough a process that is very well known and need not be described herein any detail. One necessary step is the exposure of the inner surfaceof screen 10a with actinic energy after that surface has received acoating of a phosphor bearing photosensitive resist. That step, which isof interest to the present discussion, takes place in an exposurechamber or lighthouse 12 which is indicated in FIGS. 1 and 3. It is aconventional structure including a source (not shown) of ultravioletlight, such as a mercury arc lamp, positioned to simulate the electronbeam of the tube which is assigned to excite the particular phosphoringredient of the slurry coating. The coated faceplate, with its shadowmask 11 in position, is supported at a plurality of spaced pointsdisposed along its sealing land 10d rather than having a line contactalong the entirety of the sealing surface. This is achieved by means ofthree pads 120 secured to a shelf 12b which has an aperture or cutawayarea 12c of essentially the same size and configuration as screen 10a.The pads are located so that the faceplate, when properly installedinits exposure position, is supported at three points through theengagement of these pads with sealing surface 10d at essentially thelocation of mounting studs 10c as illustrated in FIG. 2. The supportsestablish the faceplate in a reference mode, that is to say, in a restcondition in which the faceplate experiences neither deformation nortwisting moments because the pads are positioned as described to exertequalized supporting forces at the three points of support. It is commonpractice to have vertically extending positioning posts 12d on table 12bto permit rapid and precise positioning of faceplare 10 on the exposurechamber.

The validity of this three point support of the faceplate in theexposure position has been established in that examination shows thatthe reference conditions exists when the faceplate is installed in anyof the three exposure chambers generally used in screening where theprevailing practice is to assign one such chamber to the processing ofone of the three color phosphors. In other words, it is found that thespace relation of shadow mask 11 relative to screen is essentially thesame in all three'exposure chambers which is the condition to bemaintained if beam landing errors are to be avoided or at leastminimized.

After all three color phosphors have been applied to the screen by thephotographic resist process featuring exposure of the faceplate for eachsuch phosphor, the screen is filmed and aluminized in a well knownmanner and is then ready to be sealed to the funnel section 13 of theenvelope which, as indicated in FIG. 4, is held in a generally verticalposition by means ofa sealing fixture '14 described and claimed in US.Pat. No. 3,329,422, issued July 4, 1967 in the name of Hajduk andassigned to the assignee of the present invention. The large and freeedge 13a of the funnel constitutes a second sealing land which has thesame size and configuration as land 10d of the faceplate in order thatthey may properly register with one another. The first step of thesealing operation is placing faceplate 10 on funnel l l with sealinglands 10d and 13a facing and in registration with one another, with afrit material 15 deposited between the lands, and with faceplate l0supported from funnel 13 through a plurality of spaced contacts disposedalong the sealing lands to re-establish faceplate 10 in its aforesaidreference mode. The necessary condition to be attained is reestablishingthe faceplate in its reference mode and this condition may be satisfiedin a variety of different ways. For example, high spots may be providedin the sealing land of either faceplate 10 or funnel l3; alternatively,particularly when processing a tube having an envelope of conventionalconstruction, shims or othersupport elements may be positioned at theproper locations on sealing land 13a before the faceplate is placed onthat land. FIG. 4 illustrates this approach in which shims 16 of verysmall area are placed on sealing land 13a to engage land d of thefaceplate preferably at the same spaced points at which the faceplatewas supported during exposure. An important consideration is that theenvelope sections 10 and 13 are supported at spaced points chosen toestablish the faceplate in its reference mode as distinguished from pastpractices wherein the sealing lands are in line or continuous contactwith one another. The shims 16 may be ballpoints, small glass rodsegments or any material which affords the necessary mechanical supportof the faceplate and is compatible with the envelope sections and thesealing material applied to these component parts to effect a vacuumtype seal between them. Usually, a frit-seal composition is applied tosealing land 13a and also to all surfaces of shim 16 after whichfaceplate 10 is placed upon the shims. The envelope is now ready forsealing and this is accomplished by subjecting the assembly to heattreatment in a lehr having the appropriate temperature profile and timecycle to seal the faceplate and funnel to one another along the entiretyof the sealing lands. Of course, the material of which shims 16 areformed must retain its mechanical and physical integrity during the heattreatment or sealing process. For a 23 inch rectangular tube the shimsmay be formed of glass or ceramic having the same thermal expansioncoefficient as the funnel glass. The shims should be electricalinsulators and present a support area of approximately 0.0625 squareinch and a height of approximately 0.015 inch. Satisfactory results havebeen obtained through the use of glass rod segments having a diameter of0.015 inch and a length of 0.5 inch. Flat shims, having a support areaof 0.25 X 0.25 inch and a thickness of 0.015 inch, are also suitable.

FIG. 6 represents a novel form of funnel 13 which has raised elementalareas 16a on its sealing land at places corresponding to the locationsof shims 16 in FIG. 4. This is an approach in which the spaced supportsare formed integrally with. the funnel and this may be achieved bymolding orby grinding in fabricating the funnel.

Measurements have been made of color picture tubes fabricated inaccordance with the present invention which verify the efficacy of thedescribed process in reducing beam landing errors attributable todeformation of the faceplate in sealing. By supporting the faceplate atspaced points relative to the funnel, rather than having them in linecontact, one is able to establish the faceplate in its reference modeand the desired spaced relation to mask 11 relative to screen 10a ispreserved to a much higher degree of accuracy than with prior practicesin which sealing lands of the faceplate and funnel engage in linecontact. Because of the property of elasticity exhibited by the facepanel, the line contact of these envelope sections permits the panelflange to accommodate to the funnel and in a great many instances resultin an undesirable change in the mask to screen space relation, leadingto beam landing errors. Practicing the present invention not onlyreduces the change in mask to screen spacing but is further attractivein that it makes unnecessary the expense of prior procedures in grindingthe landing surfaces of the envelope sections.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and, therefore, the aim in the appended claims isto cover all such changes and modifications as fall within the truespirit and scope of the invention.

I claim: 1. In the processing of a color cathoderay tube which has acolor-selection electrode and a multisection envelope comprised of afaceplate and a funnel, said faceplate including a screen and acircumscribing flange having provisions for mechanically supporting saidelectrode and further having an edge portion constituting a firstsealing land of a given size and configuration and said funnel having anedge portion constituting a second sealing land of said size andconfiguration, the steps which include:

photographically printing on said screen a pattern of different phosphormaterials in the application of which said faceplate with said electrodepositioned within it is exposed to actinic energy while supported atthree spaced points disposed along said first sealing land to establisha reference mode in which said faceplate is free of twisting moments;

positioning said funnel substantially vertically with said secondsealing land uppermost; placing said faceplate on said funnel with saidsealing lands facing and in registration with one another, with a fritsealing material deposited between said lands, and with said faceplatesupported from said funnel through a plurality of spaced contactsdisposed along the surface of said sealing lands to reestablish saidfaceplate in said reference mode;

and subjecting the assembly to a heat treatment to seal said faceplateand said funnel to one another along the entirety of said sealing lands.

2. The processing of a color cathode-ray tube in accordance with claim 1in which said faceplate is supported from saidfunnel at three spacedpoints disposed along said sealing lands and corresponding to said threespaced points supporting said faceplate during exposure in said printingstep.

3. The process of a color cathode-ray tube in accordance with claim 2 inwhich three support elements are inserted between said facing sealinglands to support said faceplate from said funnel.

4. In the processing of a color cathode-ray tube which has acolor-selection electrode and a multisection envelope comprised of afaceplate and a funnel, said faceplate including ascreen and an edgeportion constituting a first sealing land of a given size andconfiguration and said funnel having an edge portion constituting asecond sealing land of said size and configuration, the steps whichinclude:

photographically printing on said screen a pattern of different phosphormaterials in the application of which said faceplate with said electrodepositioned adjacent it is exposed to actinic energy while supported atthree spaced points disposed along said I first sealing land toestablish a reference mode in which said faceplate is free of twistingmoments; positioning said funnel substantially vertically with saidsecond sealing land uppermost;

placing said faceplate on said funnel with said sealing lands facing andin registration with one another, with a frit sealing material depositedbetween said lands, and with said faceplate supported from said funnelthrough a plurality of spaced contacts disposed along the surface ofsaid sealing lands to reestablish said faceplate in said reference mode;and subjecting the assembly to a heat treatment to seal said faceplateand said funnel to one another along the entirety of said sealing lands.

1. In the processing of a color cathode-ray tube which has acolor-selection electrode and a multisection envelope comprised of afaceplate and a funnel, said faceplate including a screen and acircumscribing flange having provisions for mechanically supporting saidelectrode and further having an edge portion constituting a firstsealing land of a given size and configuration and said funnel having anedge portion constituting a second sealing land of said size andconfiguration, the steps which include: photographically printing onsaid screen a pattern of different phosphor materials in the applicationof which said faceplate with said electrode positioned within it isexposed to actinic energy while supported at three spaced pointsdisposed along said first sealing land to establish a reference mode inwhich said faceplate is free of twisting moments; positioning saidfunnel substantially vertically with said second sealing land uppermost;placing said faceplate on said funnel with said seAling lands facing andin registration with one another, with a frit sealing material depositedbetween said lands, and with said faceplate supported from said funnelthrough a plurality of spaced contacts disposed along the surface ofsaid sealing lands to re-establish said faceplate in said referencemode; and subjecting the assembly to a heat treatment to seal saidfaceplate and said funnel to one another along the entirety of saidsealing lands.
 2. The processing of a color cathode-ray tube inaccordance with claim 1 in which said faceplate is supported from saidfunnel at three spaced points disposed along said sealing lands andcorresponding to said three spaced points supporting said faceplateduring exposure in said printing step.
 3. The process of a colorcathode-ray tube in accordance with claim 2 in which three supportelements are inserted between said facing sealing lands to support saidfaceplate from said funnel.
 4. In the processing of a color cathode-raytube which has a color-selection electrode and a multisection envelopecomprised of a faceplate and a funnel, said faceplate including a screenand an edge portion constituting a first sealing land of a given sizeand configuration and said funnel having an edge portion constituting asecond sealing land of said size and configuration, the steps whichinclude: photographically printing on said screen a pattern of differentphosphor materials in the application of which said faceplate with saidelectrode positioned adjacent it is exposed to actinic energy whilesupported at three spaced points disposed along said first sealing landto establish a reference mode in which said faceplate is free oftwisting moments; positioning said funnel substantially vertically withsaid second sealing land uppermost; placing said faceplate on saidfunnel with said sealing lands facing and in registration with oneanother, with a frit sealing material deposited between said lands, andwith said faceplate supported from said funnel through a plurality ofspaced contacts disposed along the surface of said sealing lands tore-establish said faceplate in said reference mode; and subjecting theassembly to a heat treatment to seal said faceplate and said funnel toone another along the entirety of said sealing lands.